1. Field of the Invention
The present invention relates to a coatable composition for use in masking a surface. For example, the composition of the invention may be utilized to apply a mask to an undamaged painted surface of a vehicle (or to a glass, metal or other surface of a vehicle) to protect that portion of the vehicle from paint overspray during automobile repair shop painting of an adjacent (for example repaired) portion of the same vehicle.
2. Related Art
Portions of a vehicle adjacent to the area to be painted are generally "masked" to inhibit paint overspray from reaching and adhering to areas not intended to be painted. One typical masking or protective procedure involves applying a paper mask or plastic mask over the area not to be painted. Such masks can be applied and secured by tape or similar means. They are generally stripped from the vehicle and discarded after use. However, neither of these methods is fully acceptable at least because air currents can cause the paper or plastic to flutter and allow overspray to swirl behind the paper or plastic, or to tear and expose areas to the overspray.
Water-washable liquid masking compositions have been developed. Examples of such compositions are disclosed in U.S. Pat. Nos. 5,104,711; 5,028,350; 4,525,501; and 4,347,266. The system described in the '711 patent provides an example of such systems. According to the disclosure, the liquid masking composition comprises: solvent (typically water), a surfactant, a thickener or film former (typically xanthan gum), which provides desired rheological properties and which forms a film on the coated surface and surfactant, and a polyhydroxy liquid carrier (typically glycerol), which aids in dispersion of thickener and surfactant during formulation of the composition and which also operates as a plasticizer in the final coating. The composition is typically prepared by mixing together appropriate amounts of the various components. A portion of a vehicle to be masked is then spray-coated (typically and preferably with an atomizing spray gun) with the liquid masking composition. As the masking solution spreads, it will form a continuous "mask," i.e., a film or coating. A portion of the vehicle (not coated with film) to be finished is then coated with automotive primer, paint, or enamel, with any overspray that occurs typically landing on the masking film. After painting is complete and the paint film is dry, the masking film is readily removed with a washing solution, typically water or soapy water.
Previously used glycerol-based masking compositions have a tendency to mar, soften, and create hazing in the underlying paint film particularly after exposure to high temperature for prolonged periods of time.
While there have been some limited successes in providing effective protection with conventional masking compositions, some problems have been observed. In particular, in some applications when the masking film is washed off, a residue is observed to remain on the painted, previously masked, surface. While such residue can take a variety of forms, it is often observed to be a plurality of light-colored spots of residue. The presence of such residue on surfaces previously masked with liquid masking compositions is generally referred to as "spotting."
Problems with spotting are often associated with dissolved solids in the water used in the coating and counterions of anionic surfactants used to promote wetting and levelling of the coating. Spotting problems have been observed to be reduced through the use of deionized water and non-ionic surfactants in masking compositions.
Minimizing presence of the problem ionic components or reducing their ability to form precipitates has had some benefit. However, spotting has continued to be a problem, even when compositions involving improved surfactants, deionized water, and in some instances various sequestering agents are utilized.
It has been observed that problem spotting does not take place with equal frequency in all types of applications, to all types and colors of vehicles, in all environments. In particular, it is observed that problem spotting appears to be most persistent on dark-colored vehicles, although that observation may at least in part reflect the fact that spotting is much easier to detect when contrasted with a dark finish. Also, persistent spotting problems appear to be more likely to occur in warmer seasons or climates.
Upon close examination, it was observed that the persistent "spotting" problems were more than merely the generation of a surface deposit on the vehicle paint. It appeared that the spot causing residue had a component which reflected destruction of, or damage to, the paint on the vehicle.
In particular, vehicles, after having been coated with the masking solution, may be left out in the sun for a period of time to dry. Spotting appears to be most persistent on dark-colored cars treated in hotter environments. Darker-colored vehicles will tend to absorb a greater amount of energy and become hotter. The surface temperature of a dark-colored automobile can readily get to 80.degree.-95.degree. C., and some believe up to as high as 135.degree. C., on especially hot, sunny days. Lighter-colored vehicles, of course, will not absorb as much thermal energy, and thus may not become as hot.